Oracle Linux 7.x's default user environment, Gnome, uses hardware acceleration to render the graphics. Therefore, when remotely connecting with Xmanager, you may not be able to access the the desktop user environment or if you are able to connect, it will run very slowly.

As such, you will have to use a different user environment than Gnome and a different XDMCP Daemon than gdm.

Use the following instructions to install lightdm and Xfce (or KDE) as the XDMCP Daemon and desktop user environment to connect to RHEL 7. These instructions require root privileges. Be extra careful when making configurations with root privileges.

Red Hat Enterprise Linux's default user environment, Gnome, uses hardware acceleration to render the graphics. Therefore, when remotely connecting with Xmanager, you may not be able to access the the desktop user environment or if you are able to connect, it will run very slowly.

As such, you will have to use a different user environment than Gnome and a different XDMCP Daemon than gdm.

Use the following instructions to install lightdm and Xfce (or KDE) as the XDMCP Daemon and desktop user environment to connect to RHEL 7. These instructions require root privileges. Be extra careful when making configurations with root privileges.

Gnome in CentOS 7 tries to use local hardware acceleration and this becomes a problem when trying to connect remotely using XDMCP. To avoid this problem, you have to use an alternative display manager (other than ‘gdm’) and desktop environment.

This guide explains how you can change the display manager to lightdm from gdm and desktop environment from Gnome to Xfce. You will require root privileges. Be extra careful when making any configurations with root privileges.

Switching Display Manager from gdm to lightdm

Switch to root account and install lightdm:

# yum install lightdm

If lightdm cannot be installed because of the system's default repository, extra repository information, EPEL (Extra Packages for Enterprise Linus), is required.

The above versions of Ubuntu's default user environment, Gnome(Ubuntu), use hardware acceleration to render the graphics. Therefore, when remotely connecting with Xmanager, you may not be able to access the the desktop user environment or if you are able to connect, it will run very slowly.

As such, if you are using the above Ubuntu versions, you will have to use a different desktop user environment.

Use the following instructions to install Xfce as the desktop user environment so you may connect to Ubuntu. These instructions require root privileges or the sudo command. Be extra careful when making configurations with root privileges.

XDMCP Configuration

LightDM Configuration

Configure the /etc/lightdm/lightdm.conf file as follows. If the file does not exist, create it.

[XDMCPserver]enabled=true

Firewall Configuration

Open UDP port 177 from the PC to the remote host direction.Open incoming TCP ports 6000~6010 from the remote host to your PC

f you wish to temporarily remove the firewall to identify an issue, you can use the 'iptables -F' command. By default, iptables is not enabled on Ubuntu. Use the iptables -L command to verify whether or not it is running. For more information on the firewall consult your Ubuntu manual or contact Ubuntu technical support.

Restart XDMCP service daemon

Reboot your Linux machine or run the following command:

$ sudo service lightdm restart

Create Xmanager session

When using LightDM, there may not be a response to an XDMCP broadcast. Therefore, depending on the Xmanager version, the sessions may not appear on Xbrowser's list. If this is the case, try creating a new XDMCP session through the File menu or directly inputting the IP Address or Host Name in the address bar.

Installing the Xfce Desktop Environment

Install a new user desktop environment (Xfce)

$ sudo apt-get update$ sudo apt-get install xubuntu desktop

Apply the new user desktop environment by restarting the XDMCP daemon

$ sudo service lightdm restart

After connecting with Xmanager, select the Xfce or Xubuntu session from the login screen

The above versions of Fedora's default user environment, Gnome, uses hardware acceleration to render the graphics. Therefore, when remotely connecting with Xmanager, you may not be able to access the the desktop user environment or if you are able to connect, it will run very slowly.

As such, you will have to use a different user environment than Gnome and a different XDMCP Daemon than gdm.

Use the following instructions to install lightdm and Xfce (or KDE) as the XDMCP Daemon and desktop user environment to connect to Fedora 18, 19, or 20. These instructions require root privileges. Be extra careful when making configurations with root privileges.

User Desktop Environment Configuration

Install New Desktop User Environment (Choose one or the other)

Xfce Installation (lightdm will be installed as well)

# yum groupinstall xfce

KDE Installation (kdm will be installed as well)

# yum groupinstall kde-desktop

XDMCP Configuration

lightdm Configuration

Configure the /etc/lightdm/lightdm.conf file as follows. (If the file does not exist, create it.)

[XDMCPServer]
enabled=true

kdm Configuration

Configure the /etc/kde/kdmm/kdmrc file as follows. (If the file does not exist, create it.)

[Xdmcp]
Enable=true

Apply and Restart XDMCP Service Daemon

# systemctl disable gdm ; systemctl enable lightdm(or kdm)

# systemctl stop gdm# systemctl start lightdm(or kdm)

Temporarily Disable Firewall to Test Configuration

# systemctl stop firewalld.service

Open UDP port 177 from the PC to the remote host direction. For further firewall support, consult your OS manual.